Material handling is an important, and even crucial, component of the overall automation of a manufacturing or assembly operation. Typically, an assembly or manufacturing operation is carried out at a series of work stations, each work station being dedicated to one or a few functions which are required in order to complete the manufacturing operation. In a large number of instances the work stations may be automated, although as will appear below, that is not essential to the invention. Material handling functions required in a manufacturing or assembly operation require that different components be selectly delivered to different work stations at such a rate so as to elimiante the possiblity that a work station is inoperative for lack of component parts. Typically component parts are delivered from areas dedicated for that purpose.
Periodically the carriers become empty and they must be returned to a source of additional component parts where they can be refilled and returned to the work stations. In addition, the product, in the course of its assembly or manufacture, must also be delivered from work station to work station. After the final assembly or manufacturing step, the completed product must be removed from the assembly area and directed to a packaging or shipping area. Typically the product, in the course of its assembly or manufacture, is supported on another carrier (pallet), and as a result carriers must be transported from the packaging or shipping area back to the final assembly area for the manufacture or assembly of additional products. Thus the material handling system must deal with empty and full parts carriers, empty product carriers, carriers with partially completed product, and carriers with finished product. Because the manufacture or assembly operation is serial in nature (e.g. a first process or procedure must be completed before the next process or procedure can be begun), for efficient operation the time required to effect the different procedures along a serial production or assembly line should be balanced, for the overall line can operate no faster than the slowest unit in the line. Movement of partially or fully completed product is of the highest priority because any delay in that motion leads directly to a delay in the overall production rate. On the other hand, the motion of parts carriers and empty product carriers cannot be ignored because these elements too are critical in producing the completed product.
The prior art provides a host of elements for the automated assembly facility, but does not describe how these components can be fit together to achieve the objectives of maximum through-put, flexibility, safety and inventory control, while minimizing cost, space, labor, work in process and down time. Typical of the prior art are Ossbahr U.S. Pat. No. 4,014,428; Ishizaka U.S. Pat. No. 4,035,904; Holzl U.S. Pat. No. 3,781,974; MacMunn U.S. Pat. No. 4,195,357 and Williamson U.S. Pat. No. 4,237,598. These references show a manufacturing operation wherein a plurality of work stations are arranged along a sequential production line. Sticht U.S. Pat. No. 4,369,872 is specifically directed to an assembly facility and he mentions that the conveyor line described therein transports workpieces, and he defines workpieces to include assembly parts and the pallets carrying the workpiece or assembly parts. Converse U.S. Pat. No. 2,884,113 also describes a manufacturing facility in which a conveyor carries both workpieces on which the operation or treatment has yet to be performed and workpieces upon which the operation or treatment has been completed. Several of the references employ intermediate storage between two work stations. However, these references do not treat how the motion requirements of the various different items are prioritized so that the motion of partially completed product is not inhibited or impeded by the motion of full or empty parts carriers, while at the same time ensuring that work stations are not shut down for the lack of required parts. Scourtes U.S. Pat. No. 4,144,960 describes a production system where each work station has a location to store, off the conveyor line, a single unit of work, in addition to the work item actually being worked on.
Clearly the various articles could be transported by dedicated, single purpose transporters. This approach is defective from the standpont of expense, space consumed and crowding the assembly stations. The plural single purpose transporters multiply cost, occupy excessive area, and bringing them together at each work or assembly station is difficult from two points of view. Firstly, it multiplies the assembly station area (additional space is consumed). Secondly, even if the assembly station is automated, access for an operator is required to clear jams, for maintenance, etc., the collection of a large number of transporters impedes this access.
Thus it is one object of the present invention to provide an automated assembly facility which includes an assembly line conveyor and a series of assembly station positioned along the assembly line conveyor, so that work in process can travel along the assembly line conveyor from work station to work station, and which also provides for a supply of carriers to the several assembly stations from a random storage facility wherein the random storage facility is located along the assembly line conveyor on an opposite side of the assembly line conveyor from the series of work stations and operated so that parts carriers can be located in the random storage facility opposite the work station at which they are needed. In accordance with this aspect of the invention, when any particular work station calls for an additional parts carrier, the available parts carrier in the random storage facility directly opposite the work station can be imemdiately transferred directly across the assembly line conveyor into a carrier receiving area at the work station.
In order to provide the desired production rate, a plurality of assembly lines are provided operating in parallel to each other. Since each line is associated with a random storage facility the several lines can be densely packed by placing two adjacent lines with their respective storage facilities directly adjacent each other and treating this dual line as a unit. Other such units are separated by aisles so that the assembly stations of each unit are directly adjacent a line for access. Thus a single aisle serves two lines providing for efficient space consumption.
A single random storage facility is served by a transporting means so that any storage location is accessible. A first conveyor is arranged for transporting carriers from at least two different source locations to the random storage facility. The random storage facility includes a two-dimensional array of storage locations, and an associated series of assembly stations distributed along one dimension of the storage locations. Thus the carriers transported by the first conveyor are transferred by the transporting means to selected locations in selective ones of the random storage facility, depending on the contents of the carrier. In this fashion, when a particular work station requires a new supply of parts, a new supply of parts is available in the random storage facility at the appropriate location so that the new supply of parts can be transported across the assembly line conveyor directly in to a receiving area at the work station. Carriers which have been depleted of their contents are ejected from the carrier receiving area directly onto the assembly line conveyor. Each assembly line conveyor includes, adjacent an outlet end, a coupling conveyor for transporting articles carried by said assembly line to the first conveyor. In addition to different component sources associated with the first conveyor, the first conveyor is also associated with a packaging and shipping area to which carriers with completed product are delivered. The first conveyor then carries empty product carriers from the packaging and shipping area back to the random storage facility for later transfer to a work station when needed. The packaging area is another source of carriers.
Thus the invention provides a facility for automated assembly of a product comprising:
a first conveyor for transporting carriers from at least two different source locations to a random storage facility,
said random storage facility comprising a two-dimensional array of storage locations and transporting means for moving carriers from said first conveyor into a selected storage location and for moving carriers out of a selected storage location,
an assembly line conveyor positioned adjacent to and extending along one dimension of said two-dimensional array of said storage facility,
a series of assembly stations positioned along said assemlby line conveyor opposite to said random storage facility,
at least one of said assembly stations having two carrier receiving areas located at different positions along said one dimension, and
transfer means associated with said random storage facility and assembly line conveyor and located directly opposite one of said two carrier receiving areas to trasnsfer a carrier provided to said transfer means by said transporting means directly across said assembly line conveyor into one of said carrier receiving areas.
Typically the assembly station includes a work area and one or more carrier receiving areas. The work area may be occupied by a carrier or pallet for work in process, and one or more of the carrier receiving areas may locate other (component carrying) carriers. Components then are transferred from a carrier and placed on the work in process. The work in process carrier is then ejected onto the assembly line conveyor for transport to the next assembly station. Carriers depleted of components are also ejected onto the assembly line conveyor for transport via the coupling conveyor back to the first conveyor. Completed product carrying pallets are also ejected onto the assembly line conveyor and transported, from an outlet end of the assembly line conveyor via the coupling conveyor to the first conveyor. In the case of empty parts carriers, these are transported by the first conveyor back to a sub-assembly or source area wherein they can be refilled. Completed product is transported by the first conveyor to a packaging and shipping area, and empty carriers return from the packaging and shipping area via the first conveyor back to the random storage facility.